We discuss calculation of sensitivity of the response functions to a small variation of (complex) conductivity distribution of 3D model of the earth. Sensitivity calculation is an important part of almost any contemporary inverse solver. For 1D case it is possible to write a chain rule for the derivatives and calculate them together with the solution of forward problem. The other possibility is numerical differentiation. For the 2D case only the second possibility remains. For 3D numerical differentiation is too much cumbersome. However there is one more way to calculate sensitivities. It is so-called adjoint method. We explain how to apply the adjoint method to any desired response function type.